1. Field of the Invention
The present invention pertains generally to wireless locating finding methods and systems, and more particularly to a method and apparatus for detecting multipath components, estimating the number of overlapping multipath components, and providing an accurate estimate of the time and amplitude of arrival of the first arriving overlapping multipath components (rays). Such resolving is vital for obtaining an accurate location estimate in wireless-location finding systems.
2. Description of the Background Art
Wireless location finding or simply “wireless location” refers to obtaining the position information of a mobile subscriber in a cellular environment. Such position information is usually given in terms of geographic coordinates of the mobile subscriber with respect to a reference point. Wireless location is also commonly termed mobile-positioning, radiolocation, and geolocation.
Wireless location is an important public safety feature of future cellular systems since it can add a number of important services to the capabilities of such systems. Among these services and applications of wireless location are:
(a) E-911. A high percentage of emergency 911 (E-911) calls nowadays come from mobile phones. However, these wireless E-911 calls do not get the same quality of emergency assistance that fixed-network E-911 calls enjoy. This is due to the unknown location of the wireless E-911 caller. To face this problem, the Federal Communications Commission (FCC) issued an order on Jul. 12, 1996, which required all wireless service providers to report accurate mobile station (MS) location to the E-911 operator at the public safety answering point (PSAP). According to the FCC order, it is mandated that within five years from the effective date of the order (Oct. 1, 1996), wireless service providers must convey to the PSAP the location of the MS within 100 meters of its actual location for at least 67 percent of all wireless E-911 calls (the original requirement was 125 meters, but was later tightened to 100 meters). It is also expected that the FCC will further tighten the required location accuracy level in the recent future. This FCC mandate has motivated research efforts towards developing accurate wireless location algorithms.
(b) Location sensitive billing. Using accurate location information of wireless users, wireless service providers can offer variable-rate call plans that are based on the caller location. For example, the cell-phone call rate might vary according to whether the call was made at home, in the office, or on the road. This will enable wireless service providers to offer competitive rate packages to those of wire-line phone companies.
(c) Fraud protection. Cellular phone fraud has attained a notorious level, which serves to increase the usage and operation costs of cellular networks. This cost increase is directly passed to the consumer in the form of higher service rates. Furthermore, cellular fraud weakens the consumer confidence in wireless services. Wireless location technology can be effective in combating cellular fraud since it can enable pinpointing perpetrators.
(d) Person/asset tracking. Wireless location technology can provide advanced public safety applications including locating and retrieving lost children, Alzheimer patients, or even pets. It could also be used to track valuable assets such as vehicles or laptops that might be lost or stolen. Furthermore, wireless location systems could be used to monitor and record the location of dangerous criminals.
(e) Fleet management. Many fleet operators, such as police force, emergency vehicles, and other services including shuttle and taxi companies, can make use of the wireless location technology to track and operate their vehicles in an efficient way in order to minimize response times.
(f) Intelligent transportation systems. A large number of drivers on road or highways carry cellular phones while driving. The wireless location technology can serve to track these phones, thus transforming them into sources of real-time traffic information that can be used to enhance transportation safety.
(g) Cellular system design and management. Using information gathered from wireless location systems, cellular network planners could improve the cell planning of the wireless network based on call/location statistics. Improved channel allocation could be based on the location of active users.
(h) Mobile yellow pages. Based on the available location information, a mobile user could obtain road information of the nearest resource the user might need such as a gas station or a hospital. Thus, a cellular phone will act as smart handy mobile yellow pages on demand. Furthermore, the cellular user could obtain real-time traffic information based on location.
Wireless location technologies fall into two main categories: mobile-based and network-based techniques. In mobile-based location systems, the mobile station determines its own location by measuring signal parameters of an external system, which can be the signals of cellular base stations or satellite signals of the Global Positioning System (GPS). On the other hand, network-based location systems determine the position of the mobile station by measuring its signal parameters when received at the network cellular base stations. Thus, in the later type of wireless location systems, the mobile station plays no role in the location process.